1. Field of the Invention
The present invention pertains to conveyor belts used in chillers and in particular to endless conveyor belts having a transition between a straight-line path section and a generally helical or spiral path section with one or more arrangements for eliminating disturbance to food products carried on the conveyor belt at the point of transition.
2. Description of the Prior Art
Several conveyor belt arrangements are currently in use for transporting food or other products through a chiller typically including an insulated enclosure for maintaining temperatures which are below ambient temperature. In order to provide a longer path length within an insulated enclosure of minimal volume and external surface area, the conveyor belt transporting products through the enclosure is frequently made to traverse one or more helical paths or what are generally termed "spiral" paths in the industry. Accordingly, the conveyor belts experience a change in configuration, particularly along their inner and outer edges, at the point of transition where the straight-line path section of the conveyor belt enters the helical path section. To date, conveyor belts have either undergone a contraction along their inner edge or undergone contraction and expansion along their inner and outer edges, respectively.
Several problems arise when a conveyor belt bearing relatively delicate products, such as meat patties, undergoes a contraction. Meat patties, for example, have been observed to adhere to a conveyor belt upper surface at the point of entrance to chilling enclosure. Subsequent contraction of the conveyor belt often causes damage or distortion to the bottom surface of the patty in contact with the conveyor belt. Accordingly, it is desirable to reduce or eliminate such distortion and surface damage, particularly since this frequently causes the frozen food to be rejected. Other problems arise because of belt contraction; for example, contraction of a conveyor belt might bring adjacent products into contact with one another and cause distortion. To help reduce the possibility of such contact, food products loaded upstream of the helical section are often spaced far enough apart to assure that contact is not made at the transition point where the belt assumes a helical configuration. This, however, significantly reduces the product loading density on the conveyor belt, thereby reducing the throughput of a chiller apparatus and creating other potential difficulties in a liquid cryogen freezer where liquid cryogen is sprayed onto products carried by the belt in the straight line in-feed section. To make most efficient use of cooling potential of a liquid cryogen or of CO.sub.2 snow. It is considered important that the latent heat, absorbed to cause the transformation of the cryogen to its vapor state, be obtained directly from the surface of the item being frozen. Therefore if the product is unable to cover the belt as completely as possible because of the need to allow spacing between items to accommodate such reduction in surface area at the point of transition, additional of the sprayed cryogen will have to absorb its latent heat from the recirculating vapor instead of desirably extracting it directly from the items being frozen.
In an attempt to reduce problem of food distortion or surface damage at the transition point of a conveyor belt, the product may be strengthened by localized freezing, concentrated at the product's bottom surface. Using this technique, the bottom surface of a food product is made rigid enough to break adherence at its point of contact with the conveyor belt as the belt undergoes contraction at the point of transition to the helical configuration. However, such initial preparations require costly added equipment which consumes valuable floor space at the chiller entrance.
Other problems are experienced at a point of transition where a conveyor belt partially collapses to assume a helical configuration. Typically, the transition point is located immediately downstream of a product loading station, where product units are loaded on a straight section of the conveyor belt. Typically, products are loaded onto the conveyor belt from a separate loading belt, the speed of which must be matched to the speed of the conveyor belt so as to space the food products at desired intervals along the conveyor belt. At present, the most satisfactory method of matching the loading belt and conveyor belt speeds is by observing the spacing of the product units at a point downstream of the loading belt. While this method is generally satisfactory for straight-line or "tunnel-type" conveyor belts not undergoing a transition, direct visual observation in chillers having helical path sections is typically quite difficult, and accordingly, the need for adjustments in product spacing is indicated only after the product units emerge from the chiller enclosure. Thus, complete loading of a conveyor belt must oftentimes be delayed until a few sample product units have traversed the entire path through the chiller enclosure and sometimes several iterations of spacing adjustments may be needed before satisfaction is achieved.